Vascular disorders and defects such as aneurysms and other arteriovenous malformations often occur near the junction of large arteries, for instance at the base of the brain in the Circle of Willis. As aneurysms develop they typically form as a saccular aneurysm protruding from a wall of a vessel and have a neck and a dome portion. Alternatively, aneurysms can form as fusiform malformations that balloon a cross-section of the affected vessel.
Aneurysms and other malformations are especially difficult to treat when located near critical tissue or where ready access to the malformation is not available. Both difficulty factors apply especially to cranial aneurysms. Due to sensitive brain tissue surrounding cranial blood vessels, it is challenging and risky to surgically treat defects of the cranial vasculature.
Alternatives to surgical procedures include endovascular delivery through a catheter delivery device of an intravascular implant, such as an occlusive device in the form of a tubular, self-expanding stent. In one such procedure, an intravascular implant is stored in the distal end of a delivery catheter. The distal end is initially inserted into non-cranial vasculature of a patient, typically a femoral artery in the groin, and guided to the aneurysm. Once the distal end of the catheter is positioned, the stent is advanced, or pushed, distally through the catheter using a pushing surface within the catheter. As the stent is advanced it emerges out of the catheter and self-expands in its current location in the vessel. Such a delivery mechanism is a push-only system; the delivery mechanism pushes the stent out of the catheter, but the stent cannot be moved in the opposite direction within the catheter.
Other mechanisms include dual bumper systems where a stent is radially compressed between two pushing surfaces, one proximal and one distal of the stent. While the entirety of the stent remains within the catheter, the stent can be advanced and retracted in the catheter. However, if the distal portion of the stent is advanced beyond the tip of the catheter, the ability to retract the stent is lost as the diameter of the stent grows to exceed that of the distal most bumper. At this point, the system is a push-only system. Another type of delivery mechanism requires a certain feature to be included on the proximal end of the stent. The delivery mechanism captures the feature on the proximal portion of the stent so that it can be advanced and retracted. Although potentially useful, it is not always feasible or practical to provide such features on a stent.
Accordingly, there remains a need for improved methods and devices that effectively deliver an intravascular implant and allow for a greater degree of manipulation of the intravascular implant.